Intelligent Network (IN) services have become commonplace in modern telephone systems. Such IN services greatly enhance the functionality of telephone systems beyond the classical concept of simply connecting a call originating terminal with a call destination terminal. The “intelligence” of an intelligent network consists in the capability of identifying certain calls as associated with certain services, such as call forwarding, call queuing, call holding, etc. The basic concept of intelligent network services is well known in the art and need not be described further here.
One way of providing an IN technique that is flexible by not being fixedly bound to a telephone standard, is to provide a call handler that is arranged to receive network calls and apply routing information to such calls, where said call handler also checks if an IN service is to be invoked for a call, and if it is decided that an IN service is to be invoked, sending appropriate signals to an intelligent network service handler, which will then perform processing for providing the intelligent network service. Providing IN services is especially popular in mobile telephone systems, and since competition in the field of mobile telephony is hard, mobile telephone operators want to achieve a competitive advantage over other operators by offering their own services, which are not specified by standards. For mobile telephone systems, the known technique of Customized Applications for Mobile network Enhanced Logic (CAMEL) is one example of a standardized way of offering IN techniques for mobile networks. CAMEL is designed for use with GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telephone Standard).
FIG. 3 shows a basic arrangement of a call handling system according to CAMEL. A GSM network 30 contains a gateway mobile switching center (GMSC) 10. Network 30 could equally well be a UMTS network. Reference numeral 100 indicates a call provided to the GMSC 10, such that routing information can be applied to said call. In order to do this, the GMSC 10 interrogates the home location register (HLR) 11, which stores information that relates to call destination information contained in a call being routed. Namely, the home location register 11 contains information associated with a given subscriber, and a call being routed contains information relating to a given subscriber. Typically this will be the directory number assigned to said subscriber. The GMSC 10 will then request routing information associated with said directory number by sending an appropriate signal 101 to the HLR 11. In GSM such a signal is also referred to as a send routing information (SRI) MAP message. The HLR 11 then sends back appropriate routing information with a signal 102. This routing information can be a simple roaming number, i.e. a number which identifies the mobile switching center (MSC) presently serving the identified mobile subscriber. On the other hand, if an appropriate IN identifier is activated for the given subscriber, then the HLR 11 will provide IN invocation information to the GMSC 10.
If no IN invocation information is contained in signal 102, then the normal routing information (e.g. the roaming number) is applied to the call and this call is placed back into the network, which is indicated by arrow 107. It may be noted that full arrows represent content and signaling, while dotted arrows represent only signaling in FIG. 3.
If IN invocation information is passed to the GMSC 10, then the GMSC 10 routes the call to an entity call gsmSSF (gsm Service Switching Function) 20. In the example of FIG. 3, the GMSC 10 and gsmSSF 20 are contained in a node 200 of network 30. The gsmSSF 20 then requests information from the so-called gsmSCF (gsm Service Control Function) 21. The gsmSCF 21 instructs the gsmSSF on how to handle the call, and the appropriate IN service is executed. This is indicated by arrows 104 and 105. The gsmSSF 20 then carries out the instructions, which can e.g. consist in routing the call back to the GMSC, which in turn routes it back to the network, which is indicated by arrows 106 and 107. Naturally, this is only an example, as there is a multitude of IN services. In other words, it would also be possible that the gsmSSF 20 could hold the call while an outgoing call is started to a different subscriber, for arranging a meeting or conference.
A general problem with IN technology is the additional load in the network when all calls of IN subscribers have to be routed to the separate functional entity gsmSSF 20, and an additional procedure called IN triggering is required. IN triggering refers to the dialogue between the gsmSSF 20 and the gsmSCF 21. According to capacity calculations made with a default traffic model, an average load increase of IN invocation for a call can be quite considerable.
The second phase of the CAMEL standard (CAMEL ph2) addresses this problem by introducing a method referred to as conditional triggering. For originating calls, this method allows the gsmSSF 20 to check certain call conditions, such as dialed number, basic service code or type of call, before IN triggering. For terminating calls, this method allows the HLR 11 to check the basic service code before returning IN data to the GMSC 10. In other words, it is possible to make IN invocation dependent on the call type. An example of this could be that voice calls are forwarded, but fax calls are not.
Although conditional triggering reduces the network load, there is still a desire for greater load reduction. It may be noted that this desire not only exists in connection with the specific example shown in FIG. 3, but in connection with any system that employs a call handler (consisting of the GMSC 10 and HRL 11 in the example of FIG. 3) and an intelligent network service handler (consisting of the gsmSSF 20 and gsmSCF 21 in the example of FIG. 3), where the call handler is arranged to determine routing information and to perform an IN invocation under certain conditions.